1. Technical Field
This invention relates generally to portable electronic equipment and more particularly to controlling of the powering such equipment.
2. Description of Related Art
As is known, integrated circuits are used in a wide variety of electronic equipment, including portable, or handheld, devices. Such handheld devices include personal digital assistants (PDA), CD players, MP3 players, DVD players, AM/FM radio, a pager, cellular telephones, computer memory extension (commonly referred to as a thumb drive), etc. Each of these handheld devices include one or more integrated circuits to provide the functionality of the device. For example, a thumb drive may include an integrated circuit for interfacing with a computer (e.g., personal computer, laptop, server, workstation, etc.) via one of the ports of the computer (e.g., Universal Serial Bus, parallel port, etc.) and at least one other memory integrated circuit (e.g., flash memory). As such, when the thumb drive is coupled to a computer, data can be read from and written to the memory of the thumb drive. Accordingly, a user may store personalized information (e.g., presentations, Internet access account information, etc.) on his/her thumb drive and use any computer to access the information.
As another example, an MP3 player may include multiple integrated circuits to support the storage and playback of digitally formatted audio (i.e., formatted in accordance with the MP3 specification). As is known, one integrated circuit may be used for interfacing with a computer, another integrated circuit for generating a power supply voltage, another for processing the storage and/or playback of the digitally formatted audio data, and still another for rendering the playback of the digitally formatted audio data audible.
Integrated circuits have enabled the creation of a plethora of handheld devices, however, to be “wired” in today's electronic world, a person needs to posses multiple handheld devices. For example, one may own a cellular telephone for cellular telephone service, a PDA for scheduling, address book, etc., one or more thumb drives for extended memory functionality, an MP3 player for storage and/or playback of digitally recorded music, a radio, etc. Thus, even though a single handheld device may be relatively small, carrying multiple handheld devices on one's person can become quite burdensome.
Further, minimizing power consumption, and thus, maximizing battery life is a crucial parameter when differentiating portable products. Therefore, switching converters that utilize discrete inductors are used to efficiently produce supply voltages for the integrated circuits inside the handheld devices. The use of inductors in power conversion produces much higher efficiencies than linear regulators but require that the converter current be strictly limited below a certain threshold. This important constraint is needed to keep the inductor's inductance value from dropping significantly (i.e., want to avoid saturating the inductor). If the inductance value drops when the current exceeds this threshold, the drop in inductance can damage the portable device or even pose a safety issue. One technique to prevent saturating the inductor is to include current limiting on the outputs of a DC-to-DC converter. Current limiting is achieved by measuring the current of an output and when the current exceeds a threshold, limiting the current of the output. One approach for measuring the output current is to include a transformer in the output path. This, however, is very difficult to do on an integrated circuit and thus is not used for ICs. Another approach for measuring the current is to include a resistor in the output path and measure the voltage drop across the resistor. While this measures the current, it increases power consumption and requires additional circuitry.
Therefore, a need exists for a method and apparatus to provide current limiting of an output current of an on-chip DC-to-DC converter without an increase in power consumption and without a magnetic element.